Motor Breaker Type

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session88

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We have a 20 HP 460 VAC motor. FLA: 24 Amps. RPM: 1765. Des. B

We need to determine what will be the corrcect type and size breaker for this motor.

The old 30 Amp 3 Pole ITE Cat.# ED63A030 Instantaneous Magnetic Trip Breaker does not hold the motor. Keeps tripping. We meggered the motor and verified all of the electrical connections are tight. Nothing wrong in the field. We think that this old ITE Breaker is the wrong type.
 
If it's an MCP breaker it has an adjustable trip. Your OP appears to have omitted what it was set at. Please advise what the the MCP trip range is and what it was set at when it tripped and I think we can go from there, to see is we should re-evaluate if the beaker sould be changed of not.
I also seemed to have missed if your motor was energy efficient of not. Am I to assume that your motor is an energy efficient motor?

With more complete information solving your issue should easily be a walk in the park to determine what would solve your problem.
 
session88 said:
We have a 20 HP 460 VAC motor. FLA: 24 Amps. RPM: 1765. Des. B

We need to determine what will be the corrcect type and size breaker for this motor.

The old 30 Amp 3 Pole ITE Cat.# ED63A030 Instantaneous Magnetic Trip Breaker does not hold the motor. Keeps tripping. We meggered the motor and verified all of the electrical connections are tight. Nothing wrong in the field. We think that this old ITE Breaker is the wrong type.
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Mag only (instantaneous) CB shall part of a listed combination (CB contactor, overloads) starter. They work just fine. In fact that's my preference. Only you can look at the bucket and see if it is a listed combination starter. If it is not, then someone has wrongly installed the CB - I can't help and none of this applies.

Assumption: The CB is tripping on motor start.
So, did the old CB hold the starting current some time in the past and now does not? Or is this the first time the CB has been installed in this service?

All instantaneous CBs have adjustment dials. (note to nit pickers: Yes, I'm sure you can find plenty of screwy exceptions that don't fit the OP). The CB may say 30A on the handle (or nameplate), but the instantaneous rating will be maybe 100A to 500A (this is a guess) - dial setable. That's right, the nameplate may say 30A, and the CB will hold in forever at 500A.

For your example, I expect a setting of 200A to 300A. Look at (2011) 430.52.3. Read all of exceptions. If the CB is set below this level, set it up - Per the NEC 430.52.3

If it has held in the past, is set correctly, and now does not hold starting current, replace it with the same spec CB - and set it correctly.

If you can, get a recording meter and check the starting current. "Instantaneous" means just that - one cycle is enough. The instantaneous dials have to be set above the peak current.

ice
 
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The breaker is tripping at start up. The motor is a Baldor Super E. Premium Efficient Motor. The breaker is set at its maximum setting of 270 Amps. We assume that the Design: B implies that this is a Premium Efficient Motor.?...

This motor has been fed by this breaker for many months and until last week has not been tripping. The starter OL's do not trip. Just the breaker at start up. We are comming to the conclusion that this breaker is too small and that we need a breaker with a 297 Amp (low setting) or 459 Amps (high side) adjustable trip setting.
 
session88 said:
The breaker is tripping at start up. ....
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Good. That makes sense.

session88 said:
... This motor has been fed by this breaker for many months and until last week has not been tripping.

... We are comming to the conclusion that this breaker is too small and that we need a breaker with a 297 Amp (low setting) or 459 Amps (high side) adjustable trip setting.
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The CB worked last week and doesn't now. Okay. What changed? Nothing? Then why do you need a CB with a different rating? I'd say you have a broken CB that needs replacing. And likely the same size would work - it did last wek.

And yes, I agree, since you are replacing the CB, I likely would get one with higher inst ratings if available. Don't forget, this is a listed combination starter. If the listing (parts list) does not include the CB you want, then you either get a new bucket, or stuff in the one you want illegally.

So, how do you pick the right range:
First read 430.52.3 and the notes:

session88 said:
... The motor is a Baldor Super E. Premium Efficient Motor.

... We assume that the Design: B implies that this is a Premium Efficient Motor.? ... .
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Then look up the motor specs - don't guess.

ice
 
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session88 said:
The breaker is tripping at start up. The motor is a Baldor Super E. Premium Efficient Motor. The breaker is set at its maximum setting of 270 Amps. We assume that the Design: B implies that this is a Premium Efficient Motor.?...

I find it a bit strange that it worked for some time before it started to nuisance trip because you max setting is just not high enough.. Anyway, I think that the breaker size is too small.
This is what I would recommend would be considered as standard for you motor:
Siemens / Ite / Gould - ED63A050 - Motor Circuit Protector Circuit Breaker
•600 VAC At 50/60 Hz
•50 Ampere
•3 Pole
•Trip Setting *180 To 600* Ampere
•Motor Fla 13.84 To 54.5 Ampere

What I also recommend is that you start of with a reasonable high setting which you guess would be high enough not to cause a trip. Then you gradually reduce the setting such that it is just trips then increase the setting. That would be the optimum setting. You may get another nuisance trip which you can tweak it up a little more .
Should the motor trip the MCP in the future that would signify a change in the motor characteristics which should trigged you to megger the motor for signs of a pending motor failure.
What the MCPs were designed to do originally is to prevent catastrophic motor failure that would result in a fire. Since motors often fail as the insulation of a winding starts to go to ground you want to prevent that failing winding to get to a point of a catastrophic failure. The more damage that is done to the motor the repairs could me more costly or even destroy the motor.
As such, the best setting for an MCP is just high enough to allow the motor to start without nuisance tripping regards of with the maximum setting that is allowed.
I've dealt with hundreds and hundreds of application issues with MCP and have had the opportunity to failure analysis in the warranty return department. There actually were very few MCP failures, that is for the most part there was nothing wrong with them. More so than not when an MCP tripped when there seemed to be no other cause they blamed a defective MCP which the distributor replaced under warranty. When the replacement MCP also trips the technician either judges it as a piece of crap product or he scratched his head and actually determines that there is a problem that tripped the MCP.

As such I compliment you on doing your homework.
Also, NEMA design B has to do with the starting characteristics of the motor whether standard or energy efficient. Besign B refers to a typical (common) starting torque curve.

Oh, one last thing, I wouldn't be surprised if you motor had up to 312a inrush or 24fla x 13 which is not unusual for an energy efficient motor.
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It's a known problem from the breaker and starter mfrs. Newer motors can have instantaneious inrush currents that far exceed what they used to be, as in up to 20x FLC now. Many of the standard MCP designs used in listed motor starters no longer work. It is addressed on a case-by-case basis. You need to contact the motor starter mfr to see if they have a UL listed solution combination for this, you are technically not allowed to do this on your own in the field.

That said, I find it actually hard to believe that a UL listed motor starter mfr used a 30A MCP on a 20HP motor starter. A NEMA Size 2 starter is typically rated for 45A max, so whatever MCP it uses will never be smaller than 45A and that means the MCP would be adjustable to 450A. I believe you are trying to "modify" a NEMA Size 1 staerter, rated at 27A, that's why your MCP only goes to 270A. If so, you are trying to do something that is not supposed to be done and you should start with the properly sized equipment.
 
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